the Islamic State in Iraq and Syria (ISIS), a savage terrorist army
previously known as al-Qaida in Iraq, has routed the Iraqi army and now
controls territory from the outskirts of Aleppo in Syria to Fallujah and
Mosul in Iraq, even threatening Baghdad.

Leaving
aside the fact the whole of the Iraqi army has not collapsed, only 2
divisions, this is somewhat misleading as to the amount of control ISIL
(ISIS) has (or had) in Syria and ignores the extent to which they had
been pushed back by other rebel groups. Charles Lister, in a paper from May:

By late January 2014, ISIS had lost control of 28
separate
municipalities across Aleppo, Idlib, Hama, al-Raqqa and Deir Ezzor
governorates. Rather than suffering total defeats in these positions,
however, ISIS strategically redeployed its forces into better-defended
and more valuable positions, presumably preparing for its next move.
This came on February 2 when a large ISIS force unexpectedly
attacked and captured the financially valuable Conoco gas field (said
to be worth hundreds of thousands of dollars per week) from Jabhat
al-Nusra and allied tribal forces in Deir Ezzor. This surprise attack
[..] prompted a major counter-attack by Islamist militants (including
Jabhat al-Nusra), FSA-branded fighters, and local tribesmen, resulting
in ISIS’s near-total expulsion from the governorate by February 11.
Meanwhile, continued pressure against ISIS in northern Syria saw the
group withdraw from its positions in northern Aleppo on February 27 and
redeploy eastwards, while by March 13 it had
completely withdrawn from the northwestern governorates of Latakia and
Idlib. This left ISIS in control of parts of eastern Aleppo and,
crucially, the key transport routes leading to the jewel in ISIS’
crown: the city of al-Raqqa. There, the true face
of the organization has since become clear with harsh punishments now
being meted out, including the March 22 crucifixion of a man accused of
murder.

Even where it lost control of territory, though, ISIL
continued to play a destructive role against forces fighting the Assad
regime. It "has been blamed for several car bombings at rival group
headquarters, checkpoints, and at the Bab al-Salameh and Bab al-Hawa
border crossings with Turkey" and for the assassination of leaders from
rival groups Ahrar al-Sham and Jabhat
al-Nusra.

Jeremy Bowen reports from Aleppo (16 Jun), "Islamist fighters of different levels of radicalism dominate the rebel
side in Aleppo. In rural Aleppo, east towards Iraq, Isis territory
begins."

From a later piece by Charles Lister for the BBC
(27 Jun): "[Isis] controls large swathes of territory - stretching from
al-Bab in eastern Aleppo province in Syria to as far as Suleiman Bek
415 miles [..] away in Iraq's Salahuddin province." The map, as used on many other BBC web
pages, shows 3 towns in northern Syria under complete ISIL control,
without naming them. According to a map shown on CNN, they are, leading
North-East from Aleppo, al-Bab, Manbij and Jarabulus, near the Turkish border (*).

On
28 Jun, Al Jazeera English (AJE) reported that there had been clashes
around Deir Az Zor between ISIL and Jabhat al-Nusra and that 2 JN
commanders had deserted to ISIL.

Jabhat al-Nusra (JN) is
al-Qaeda's affiliate in Syria, Yemenis from Al Qaeda in the Arabian
Peninsula may be in northern Syria, collaborating with JN, passing on
bomb-making skills (**). According to a report by Paul Wood from Idlib (3 June 2014),
the black flag of the Islamic Front is almost indistinguishable from
that of ISIL, though IF's ideology is considerably more moderate.

So, the West may have legitimate concerns that are not limited to ISIL. But purely from a Syrian point of view,
ISIL must be distinguished from all the other groups. For the Syrian
people, who in the overwhelming majority still want to be rid of
Assad, ISIL is not on their side. Objectively, it is an element that
is against the revolutionary (anti-Assad) forces. When people talk
about "infighting among the Syrian rebels" (***), let us be clear:
fighting between the other groups is minimal; nearly all the
"infighting" is between ISIL against the rest.